The field of the present invention relates to optical scanning systems and particularly to a scanning system having an improved collection optics. The invention is especially suitable for use in a bar code scanner for reading bar codes such as those found on consumer products, most frequently the UPC code. The invention is suitable for stationary or handheld scanners.
Bar code scanners, as any optical system, require incoming light which has reflected off the target to be focused and detected by a suitable detector. Typically, the incoming light is collected by a collection mirror or a focusing lens and directed to the detector. In long range scanning applications, such as greater than six feet, the collecting proficiency of the optical system becomes critical in order to achieve effective detection. Put simply, light reaching the detector must have adequate intensity for effective detection. The intensity of light reaching the detector is dependent in part on the size of the collection mirror or the focusing lens.
In some detecting systems such as shown in U.S. Pat. No. 4,816,660, the outgoing beam and the incoming beam are "in line" that is on a common scanning structure. In such a system, a pivoting scan mirror operates both as a fold mirror for outgoing light and as a collection mirror for incoming light. Such a system may also require a beam splitter which reduces intensity of incoming light. Though it is desireable to have a large size collection mirror, the larger the collection mirror, the more massive pivoting mechanism is required to accommodate the larger mirror mass thereby further increasing the overall size and weight of the system. The size of the collection mirror is somewhat limited by the load which may be applied to the pivoting mechanism. Moreover, a larger mirror also increases power consumption of the pivoting mechanism. By contrast, a smaller mirror requires a smaller pivoting mechanism and reduces power consumption and by reducing the load on the pivoting mechanism may also enhance the mechanism's reliability.
Other systems which do not have the outgoing beam and the incoming beam reflecting off the same mirror typically have their collection system mounted off axis which may result in much larger size systems.